Dual-Accumulator Power Tool Charge Equalization for Full Power Use

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Solution Overview

Problem

Power tools with two accumulators face issues where the total power is limited by the weaker accumulator, and charge equalization is unidirectional, leading to incomplete utilization of available charge when one accumulator is discharged.

Innovation Solution

A power tool with two accumulators and separate power electronics systems, each with an inverter and charge equalization device, allows for bidirectional charge equalization and optimized power distribution based on accumulator states, using formulae for current flows and sensor data to balance charges.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If two accumulators are connected in series to provide high power, then the power output is improved, but the total working time is limited by the weaker accumulator

Engineering Contradiction:

Improvepower outputVSAvoidtotal working time

Core Design Contradiction:

PowerVSDuration of action of moving object

Solution Approach 1:

The power tool system divides the power supply into two independent accumulator units, each with its own power electronics system. This segmentation allows independent management and charge equalization between the accumulators, enabling the system to utilize the full capacity of both accumulators rather than being limited by the weaker one.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system dynamically adjusts the operating parameters by implementing bidirectional charge equalization between accumulators. The charge equalization devices modify the charge distribution parameters based on the state of each accumulator, allowing optimal power utilization and extending the total working time beyond what would be possible with unidirectional equalization.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If conventional unidirectional charge equalization is used, then the system is simpler to implement, but residual charge in discharged accumulators cannot be utilized

Engineering Contradiction:

Improvesystem complexityVSAvoidresidual charge utilization

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent implements bidirectional charge equalization, inverting the conventional unidirectional approach. Instead of charge flowing only from the stronger to the weaker accumulator, the system allows charge to flow in both directions between accumulators based on their respective states. This inversion enables complete utilization of residual charge in what would traditionally be considered the 'weaker' accumulator.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

Each accumulator is equipped with its own power electronics system and charge equalization device, making each accumulator unit multi-functional. The accumulators can independently provide power to the motor and simultaneously participate in bidirectional charge equalization, maximizing their utility and eliminating waste of residual charge.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Adaptability or versatility

If separate power electronics systems are implemented for each accumulator, then bidirectional charge equalization is enabled, but the device complexity increases

Engineering Contradiction:

Improvecharge equalization capabilityVSAvoidpower electronics system complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The power electronics system is segmented into two independent units, each associated with one accumulator. This segmentation enables bidirectional charge equalization while distributing the complexity across modular components. Each power electronics system includes its own inverter and charge equalization device, allowing independent control and management.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The motor serves as an intermediary element that connects both power electronics systems. Through the motor, charge can be transferred bidirectionally between the accumulators, enabling charge equalization without requiring a direct connection between the accumulators. This intermediary approach simplifies the overall system architecture while maintaining bidirectional capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12413079B2Power tool and method for carrying out charge equalization between accumulators in a power tool

Publication Date: 2025.09.09 HILTI AG

AI summary

A power tool having a first accumulator and a second accumulator, wherein the power tool has a first power electronics system with a first inverter and a second power electronics system with a second inverter, wherein the first inverter is electrically connected to the first accumulator and the second inverter is electrically connected to the second accumulator. The first power electronics system includes a first charge equalization device while the second power electronics system includes a second charge equalization device. The charge equalization devices are configured to carry out charge equalization between the accumulators. Furthermore, the power tool includes a device for speed control. In a second aspect, the invention relates to a method for carrying out charge equalization between two accumulators in a power tool. In this case, the charge equalization is preferably carried out by different load splitting via the charge equalization devices of the power electronics systems.